Look at the Toshiba 52XF550 with the super narrow bezel, it replaces the LX177 and the early reviews have been great at AVSforum (where everyone seems to hate everything ). It has one of the best 120Hz implementations I have seen, probably because Toshiba is a chip maker and has experience with DSPs and the like. Also the amount of control you have over all the picture settings on this TV is better than pretty much any manufacturer gives you access too, so if you have it calibrated or try to yourself you can really tweak it great. Also this has a Matte screen which I tend to prefer.
Also the Samsung 6 Series just came out and replaces the 71 series, so check that out too. No word on weather the Samsung 120Hz Triple ball effect bugs have been fixed, but the panel boasts a higher contrast and faster response time than the 71 series. The image on these is fantastic like the Toshiba as well, but it does have a glossy screen, which can be a problem for watching TV if you have a bright room in the afternoons, though actually looks better in the dark. Depending on your room/habits this might not be a concern.
The 81 series is something I would avoid for now as the TV really isn't nearly worth the price increase, especially considering it isn't 120Hz. LG will be releasing an LED competitor to the 81 soon and it will be 120Hz, and Samsung is releasing the 9 series replacement for the 81 in the fall, so its a bit of a ways off for a refresh in the LED category.
As far as the XBR4/5's go, the XBR6/7 replacements havent been officially announced yet, but they won't appear until the fall. However the Z series should be out relatively soon, and it upgrades everything over the XBR4/5, so thats worth looking into.
For receivers, Denon and Onkyo are great choices IMO. Also Pioneer and Yamaha have some pretty nice choices as well. I find theres alot of trade offs when it comes to selecting one, so it might be worth figuring out what your "must haves" are and then we might help narrow down further what you need.
My personal setup with that big of a budget would be:
Toshiba 52XF550 ($2500)
Onkyo TX-NR905 ($1700)
Leaving me:
$1000 for a Subwoofer (Id probably go with Hsu, Epic or eD here)
$1800 for speakers (which is above the range I have done any real research in)
That would be a pretty amazing setup IMO.
As far as above the fireplace goes, I agree with Yoyo. I have my TV up there, and while it looks fantastic off, while it is a bit annoying watching with more than 2 people. The most comfortable way to watch is with 1 person on each couch max because they kinda need to lay down so their head is looking up at the TV more comfortably. Once I move the 47" LCD thats up there into the bedroom and get something bigger Im moving it down and re-arranging some things.